There is only one fatal flaw (well, maybe there are several) in all the arguments for the introduction of copper-nickel mining to the state of Minnesota: This kind of mining has never been done in Minnesota. Mining iron ore does not have the toxic residue this kind of mining has. If you check out places where this kind of mining has been done, you find it has never, ever, anywhere on this planet of ours, been done without polluting neighboring waterways.
Wisconsin's Flambeau Mine was touted as an example of successful copper-nickel mining without pollution. It just took 10 years for toxic waste to reach nearby streams. Check out the Mount Polley mine disaster in British Columbia for another example.
Mining companies can say they have the technology to contain toxic waste; however, they have not done it yet.
Wisconsin has a "prove-it-first" law for this kind of mining. Hopefully Minnesota will follow that lead. Is this experimenting (because it has never been done) with centuries-lasting toxic wastes from copper-nickel mining near the Laurentian Divide? Will pollution flow both north and south?
This sounds like an idea whose time has not come. Is this an environmentally sound plan? Prove it first.